Automatic volume control



April 23, 1935. J. H. HAMMOND, JR 1,998,617

AUTOMATIC VOLUME CONTROL Filed May 12, 1950 FIG .3.

INPUT VQLTS OILVH NIV9 INPUTAVOLTS CLLVU NW0 avwemtoz Patented Apr. 23,1935 UNITED STATES PATENT o-FFicE 'AUTOMATIG VOLUME- CONTROL John"HaysHammond; In, Gloucester,'Mass., as-

"signer to 'Tlammond Holding Corporation,

Gloucester; Mass., a corporation f Delaware Application .M'ay 193e,Serial .No. 451, 52

claims. '(cL-m-iode) 'Ihis inventton relates to amplifying systemsmimore particularhr to an improved means for emtrolling the ofamplification of acsystem in accordance with the strength of the BP- 5pliedenergy. V

The invention provides a means of controlling the inputtoraspacedischarge amplifier in accondanoe with the strength of the appliedsignal. The invention relates par-.ticular-lyto a systemif-amplification which a greater ratio of amplification m1 gain isproduced for impressed signals of high intensity than torimpressed-"signals of low intensity. This invention also provides a;system of amplification .in which ratio cf amplification or bedecreased; astheintensity of the impressodlsignals isincrease'd. Y limeinvention-also consists certain new and original features ofconstruction and combinations at. pantshereinafter set forth andclaimed.

Although the novel features which are he- Bowed tobe'characteris-ticofinvention will be particularly pointed out in the claims-appendedhereto, invention itseldas to its objects and advantages, the mode ofits operationand the manner or maybe better understoodhy referring tothe tollowing description taken in connection the accompanying forming apart thereof,

Elgar 1' illustrates diagrammatically :a system constructed accordancewith this invention.

Figs. 2 and Save curvesillustnating the operation of the system. 7 p:Like reference characters denote like partsin the several figures ofthe drawing.

in the following description and m the claims, parts will :be identifiedicy specific names for con-- they are intended to he as generic in'their to similar parts as the art will-,permit.

:Reierring 'znnrepanticularly to the. drawing, m.--.lshowsa'z-microphone Mi which-.isconnected intbeprimary circuitofaiaansf'ormer (It, the seoondaryofwhieh is connected to apotentiometer J2, :fihispotentimieter is connected the input -cimcuitof. as space discharge amplifier l3, in the output circuit of r-which isthe primary of a transformer 44. Y One-half of the suacandary of thistransformer is connected through a reversing switch id to a"potentiometer Hi. This potentiometer is connected in the input circuitof aspaace discharge-amplifier 11. the output circuit of which isconnected to primary of a transformer 48. who secandarycf transfiomneris connected to input circuit of a push-pullamplifier 2i, theoutputcircuit of which is connected to the primary of a transformer .22.The secondary of this transformer is connected to a potentiometer 23,the otherside of which is connected to cutput terminals 24. Thesetenninals ,may be connected to anysuitabledevice such as a loud speaker.

The xother half of the secondary winding of the transformer 1-4connected to the input circuit of a space discharge amplifier 25in theoutput circuitof which is the primary of a transformer 26. Thesecondaryacfthistigansformer is connected to a rectifying devicefilwhich consists of two rectifier-s3 I and 32 :are connected in serieswith-:2, resistance '33. flihis resistance is also zin the input,circuit of a space discharge means, In the output circuit of this deviceis a solenoid 3.5, the core of which is connected to the movable contact-of the potentiometer H5. The solenoid is normally held in the-raisedpcsi- 20 tionhya spring 3511, (The filament and plate currents for thespace discharge means .34 are obtained from a transformer 36 which issupplied with .alternatingcurrent froma source 37.

In the operation of the form of the invention shownin Fig. .l, theenergy received by the microphone LQ controls the flow of cur-rentthrough the transformer l l. The current from the secondary of thistransformer 1] passes through the potentiometer 12 from which anydesired amount of energy maybe fed to the input circuit of the spacedischarge amplifier 13., where it isflampli- 'fiedgand fed to thetransformer l4.

Part of the energy in the secondary of this transformer passes throughthe reversing switch t5 t0 the potentiometer Hi. The energy picked up bythis device is then fed to the input circuit of the space'disc'hargemeans H. The rest of the energy from the secondary of the transformer itpasses to the input circuit .of the space discharge amplifier 25 whereit is amplified and passes through the transformer 26 to the rectifiercircuit 21. Herethecurrent is rectified and passes through theresistance 33 in the direction of the arrow. This causes a potentialdifference to be built'up across this resistance which is dependent uponthe strength of the current flowing in it. Ifno energy is beingreceived, there will be no current flowing through this resistance, andthe grid of the space-discharge means 34 will have no negative bias.This space discharge-means acting as a rectifier will then pass amaximum amount of current through'the solenoid 35, thus movingthe-contact of the potentiometer [6 to its farthest down position. Asthe energy re- 7 5 ceived increases and the current in the resistancealso increases, the negative potential on the grid of the spacedischarge means 34 will be increased thereby increasing the impedance ofthis device, which will cause a decreased amount of current to flowthrough the solenoid 35 thus allowing the contact of the potentiometerHi to move upward under the action of spring 35a in the solenoid 35. Itis thus seen that the setting of the potentiometer l6 will depend uponthe amount of energy received by the microphone ii If the switch I5 isthrown to the right, an increase of energy received by the microphoneIII will cause a decrease in the ratio of the received energy to thatapplied to amplifier 11 by the potentiometer it. This decrease of ratiowith respect to the input volts is shown by the curve in Fig. 2.designing the elements, including potentiometer 96, it is possible tovary this ratio so as to limit the output of the space discharge meansI"! to a predetermined value.

The controlled output from the amplifier I! then passes through thetransformer l8 to the push-pull amplifier 2 l where the energy is ampliand fed through the-transformerZZ to the potentiometer 23 where theamount of energy passed to the output circuit 24 may be controlledmanually. In this way it is possible to maintain the strength of theoutput signals within certain definite limits so as not to overload thereproducing apparatus, and to prevent distortion of the output of thissystem. 1

If the switch I5 is thrownto the left,{the ratio of the energy fed tothe input circuit of the space discharge means 11 with respect to theinput energy will ,be increased as the energy received by the microphonel0 increases. This is shown by the curve in Fig. 3. In this way it ispossible to expand the range of a received signal so that it produces agreater variation in the volume of the output signal than was present inthe volume of the input signal.

It is to be noted that in the above'described system the various spacedischarge devices are operated at all times at their point of maximumfiiciency and minimum distortion. 'The variation in volume in the outputis obtained by controlling the ratio of the impressed signal to theenergy applied to one of the stages of amplification. The amplificationfactors of the various discharge devices themselves remain constant atall times. The system is accordingly free from distortion and otherundesirable effects which would be present if the operatingcharacteristics of the space discharge devices themselves were alteredto vary the impedance thereof and thereby control the amplificationfactor.

It is to be understood that the term amplification ratio of theamplifier used herein, refers to the system as a whole and not to thevarious space discharge devices themselves, or to the single stages ofamplification, each of which have a constant amplification factor. Theabove systern is useful, as for example, in reproducing sound fronraphonograph record in which the volume range is normally suppressed. Agreater volume range can be obtained in theoutput of the amplifier,whereby the signal is caused to more nearly approximate that of theoriginal sound being reproduced. For this purpose the system is sooperated that an increase in signal causes an increase in the ratio ofthe energy applied to the amplifier.

From this it is seen that by prop y" The system may also be used toprevent overload of the amplifying devices, for which purpose thepotentiometer is so connected that an increase in signal strength causesa decrease in the ratio of energy applied to the amplifier. In obtainingboth of the above results the space discharge devices are at all timesoperated at their point of minimum distortion, that is, the center oftheir characteristic curves.

It is to be understood that the potentiometer l6 may have any suitabletype of winding which may differ according to the use to which it isapplied; For example, it may be desirable to have a different type ofwinding when the potentiometer is used for decreasing the volume rangeof the system than when it is used for increasing the volume range.

- It is also to be understood that while the system is shown asreceiving its energy from a microphone, it is not limited to thisdevice, but may receive its energy from other sources such as aphotoelectric cell used in connection with talking moving pictures, orfrom a phonographic pick-up device. Y i

Although only one of the various forms'in which this invention may beembodied have been shown herein, it is to be understood that the invention is not limited to any specific construe tion, but might beembodied in various forms without departing from the spirit of thefinvention or the scope of the appended claims.

What is claimed is: 1 g

1. In a system for use with a sound record, a sound record, an energytransfer device associated therewith, a translating device, meansbetween said energy transfer device and'said-translating devicecontrolled by the sound energy for varying the dynamics of the-sound,and means selectively to affect said dynamics either by expan'ding thevolume ratio or by compressing the volume ratio of the sound. a

2. In a system for transferringsoundbetween. a translating device and asound record, a translating device, a sound record, an energy transferdevice associated therewith; an amplifier between said translatingdevice and said energy transfer device, said amplifier comprisinganamplifier tube and a voltage varying device, a' control circuitgoverned by the average sound' energy for determining the voltageof saidvoltage varying device, and means for reversing the action of saidvoltage varying device with respect to said control circuit.

3. In a system for transferring sound between a translating device and asound record, a translating device, a sound record, an energy transferdevice associated therewith, an ampli fier between said translatingdevice and said 'en-' ergy transfer device, said amplifier comprising anamplifier tube having a potentiometer in its input-circuit, a reversingswitch for reversing said potentiometer with respect'to said amplifiertube, a solenoid for operating the movable contact of saidpotentiometer, and a control circuit operated by sound energy foradjusting said potentiometer in accordance with the average soundenergy.

4. In a sound reproducing system, a sound record, a pick-up devicetherefor, an amplifier fed by said pick-up device, a loud speaker fed bysaid amplifier, said amplifier comprising a potentiometer fed by saidpick-up device and an amplifier tube fed by said potentiometer, asolenoid controlling the adjustable contact of said potentiometer, acontrol circuit fed by said pick-up varying the dynamics of the soundenergy without' changing the amplification factor of said amplifier,means for deriving from said amplifier the energy thus varied andtranslating said energy, means for deriving from said energy transferdevice a component of energy proportional to the sound energy, and meansfor utilizing said last mentioned component to control the means forvarying the dynamics of the sound energy.

JOHN HAYS HAMMOND, JR.,

